The present invention relates to thin film integrated circuits and more specifically to flip chip mounted mixer and varactor diode circuits for microwave applications. The circuit generally comprises a planar semiconductor diode attached across a discontinuous conductor film line on a circuit carrier.
Microwave diode mixers are used to convert a signal at one frequency to one at a somewhat lower frequency. Varactors can be used as multipliers (to increase signal frequency), as well as tuning elements, switching circuits, and phase shifters. With either type of diode, to obtain high performance in terms of low conversion loss and noise, it is required to maximize the frequency cut off parameter of the diode, and to minimize the series (parasitic) inductance of the diode/conductor film combination. Since the frequency cut off parameter is inversely proportional to the product of the diode's spreading resistance and parasitic capacitance, it is desirable to minimize the spreading resistance and parasitic capacitance, as well as the parasitic inductance, when designing a mixer or varactor diode circuit.
The parasitic capacitance and inductance exhibited by a diode is in part a function of its mounting configuration on the conductor film circuit, and it has been observed that flip chip mounting yields lower parasitics than other mounting techniques (such as wire bonding). To facilitate flip chip mounting, the diode can include contacts comprising posts having bonding bumps which can be directly bonded to a film circuit. A design for such contacts, for example, is described in U.S. Pat. No. 3,874,918, issued Apr. 1, 1975, to M. I. Nechtow and J. Sandera, as well as in co-pending U.S. patent application Ser. No. 869,642, filed Jan. 16, 1978, by E. J. Denlinger and H. S. Veloric.
The spreading resistance exhibited by either type of microwave diode is a function of its geometry. Specifically, the spreading resistance depends in part upon the anode geometry and anode/cathode configuration.
To further reduce the parasitic capacitance and inductance of the diode, as well as to minimize its spreading resistance, the present invention has been developed.